Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrochlorocarbons (HCCs, e.g., 1,1,1-trichloroethane and carbon tetrachloride) have been used in a wide variety of solvent applications such as drying, cleaning (e.g., the removal of flux residues from printed circuit boards), and vapor degreasing. These materials have also been used in refrigeration and heat-transfer processes. However, the photolytic and homolytic reactivity at the chlorine-containing carbon sites has been shown to contribute to depletion of the earth's ozone layer. Additionally, the long atmospheric lifetime of CFCs has been linked to global warming. As a result, there has been a world-wide movement to replace CFCs.
The characteristics sought in replacements, in addition to low ozone depletion potential, typically have included boiling point ranges suitable for a variety of solvent cleaning applications, low flammability, and low toxicity. For some applications, solvent replacements should also have the ability to dissolve both hydrocarbon-based and fluorocarbon-based soils. In some embodiments, solvent replacements also have low toxicity, have no flash points (as measured by ASTM D3278-98 e-1, “Flash Point of Liquids by Small Scale Closed-Cup Apparatus”), have acceptable stability, have short atmospheric lifetimes, and have low global warming potentials.
Hydrofluoroethers (HFEs) have gained interest as replacements for CFCs and HCFCs. Generally, HFEs are chemically stable, have low toxicity, are non-flammable, and are non-ozone depleting.
In some instances, HFEs can form azeotropes with one or more co-solvents to modify or enhance the solvent characteristics of the HFE. Many azeotropes possess properties that make them useful solvents. For example, azeotropes have a constant boiling point that avoids boiling temperature drift during processing and use. In addition, when an azeotrope is used as a solvent, the properties remain constant because the composition does not change during boiling or reflux. Azeotropes that are used as solvents also can be recovered conveniently by distillation.